Lagos authorities said they had requested the flight's manifest to contact the other passengers, and began distributing protective clothing to health workers. Photograph: Cellou Binani/AFP/Getty Images

A man has died of ebola in Lagos, the first confirmed case of the highly contagious and deadly virus in Africa's most populous metropolis.

Patrick Sawyer, a 40-year-old Liberian civil servant, collapsed on arrival in Nigeria's main airport on Sunday, health officials said. His condition rapidly deteriorated before he died, said Abdulsalami Nasidi, project director at the Nigeria Centre for Disease Control, who attributed his death to ebola.

Officials at the World Health Organisation confirmed a sample from Nigeria was being tested for ebola, but did not confirm the results.

The pathogen is passed through contact with bodily fluids of infected patients, and has no known cure, although chances of survival improve dramatically with early detection and treatment.

But weak health systems and frequent cross-border travel have hampered efforts to contain the virus in a region which has never before experienced an outbreak.

Lagos state authorities said they had requested the flight's manifest to contact the other passengers, and began distributing protective clothing to health workers, state health advisor Yewande Adeshina said. Sawyer flew from Liberia's capital of Monrovia, with a brief flight stopover in nearby Togo. His sister is believed to have died of ebola in the last month, a Liberian official told the Guardian.

Rumours about the virus – which causes a painful fever that degenerates into internal and external bleeding – were met with scepticism from residents in the crowded business district where Sawyer was treated. "I cannot believe it is true," said trader Segun Kosoko, who said he had seen two traders donning face masks.

Experts have also been alarmed by the disease's wide geographical spread, from Guinea's remote interior forest region, where it originated, to densely populated coastal regions.

Ghana has had several unconfirmed scares, while Sierra Leone's capital Freetown recorded its first confirmed case this week. Authorities there were forced to launch a public appeal after the victim slipped out of hospital. Her family forcibly removed her – as many have done, either fearing they would catch the disease while in quarantine, or doubting its existence.

Radio stations in Freetown, a city of about 1 million people, broadcast the appeal to locate the woman, named as Saudatu Koroma. "She is a positive case and her being out there is a risk to all. We need the public to help us locate her," the appeal stated.

Koroma, 32, had been admitted to an isolation ward while blood samples were tested for the virus, said Sidi Yahya Tunis, a health ministry spokesman.

Meanwhile in Liberia this week, a man burned down a room in the ministry of health after his 14-year-old relative died of ebola. He said a lack of doctors and nurses – many of whom have been ostracised from their communities – had led to the boy's death.

Nigeria's ministry of health urged residents to follow guidelines to prevent the virus' spread, and launched a hotline number.